Asthma: acute exacerbation: magnesium sulfate reduces hospital admissions in severe cases

Clinical bottom line (level 1a)

  1. Patients with acute severe asthma who receive magnesium sulfate compared with placebo are less likely to be admitted to hospital (NNT = 2 at 2 hours) .
  2. There is no clear effect on hospital admission rate or improvement in PEFR in patients with mild or moderate asthma.
  3. Patients with severe asthma have an improvement in their %predicted PEFR of 17%.
Rowe et al: Cochrane Library 1999; 3: -
Expires November 2002

The study

Systematic review of all randomised or quasi-randomised controlled trials of
  • Patients: adults or children presenting to an emergency department with an acute asthma exacerbation
  • Intervention: intravenous magnesium sulfate (usually a bolus over 20 minutes of 1.2 to 2 g; 25 to 100 mg/kg in children) compared with placebo
  • Outcome: admission to hospital, pulmonary function tests, adverse effects
Articles found in all languages using Cochrane Airways Review Group register based on EMBASE, MEDLINE, CINAHL, 1966 to 1998 (search terms: asthma or wheez* and emerg* or acute or status AND discharge or admi* or hospit* mag* or magnesium sulfate or MS ) and and hand-searching 20 common respiratory journals. Reference lists of primary studies and review articles were searched, and colleagues, collaborators and other trialists were contacted to other studies

Selection criteria: by 2 independent reviewers: see above
Appraisal criteria: by 2 independent reviewers using a grading system. Authors were contacted for more information where necessary.
Articles excluded if: criteria not given

7 randomised controlled trials found - 2 studies in children, and 5 in adults, involving a total of 665 patients. Data was analysed comparing adults and children, and patients with severe asthma (usually defined as PEFR < 200 ml/min and a poor response to initial therapy) and those with less severe disease.
  • Patients were routinely given steroids. Patients could be given theophylline or ipratropium in some studies.
Studies were found to be heterogeneous for hospital admission and pulmonary function tests. This disappeared when the analysis was repeated based on the severity of disease

The evidence

Outcome Time to outcome CER OR
(95% CI)		 NNT
(95% CI)
hospital admission for severe asthma hours 57/63
(90.5%)		 0.10
(0.04 to 0.27) 		2
(2 to 5)
hospital admission for mild-to-moderate asthma hours 24/116
(20.7%)		 1.36
(0.72 to 2.55) 		-18
(NNT = 21 to infinity;
NNH = 5 to infinity)

  • PEFR increase: weighted mean difference: 29 ml/min (95% CI: -3.4 to 62)
  • Severe asthma: PEFR increase: weighted mean difference: 52 ml/min (95% CI: 27 to 78)
  • Severe asthma: % predicted PEFR increase - based on a single study: weighted mean difference: 17% (95% CI: 11% to 28%)

Comments

  1. No study reported any major side-effects. One trial reported 58% of patients had minor side-effects (burning at iv site, flushing, fatigue).
  2. Children and adults appeared to respond equally well

Citation

  1. Rowe BH, Bretzlaff JA, Bourdon C, et al: Magnesium sulfate treatment for acute asthmatic exacerbations treated in the emergency department (Cochrane Review). Cochrane Library 1999; 3: -
Contributor: Chris Ball and Musab Hayatli, October 1999
Reviewer: Gerard Ryan

Clinical Question.
Patient acute asthma
Intervention or Exposure magnesium sulfate
Comparison placebo
Outcome hospital admission, PEFR